As Western countries gear up for a second wave of the coronavirus disease (COVID-19) pandemic, a new study shows that this time around, the worst-hit in terms of case numbers is the young adult age group, between 18 and 29 years. This finding could be crucial in framing dynamic public health measures, which will contain and help limit rising cases.
The study was published on the preprint server medRxiv* in November 2020.
COVID-19 cases have been rising steadily over the last few weeks in all of Europe. Many regions have reinstated nationwide lockdowns – in Italy, Belgium and the United Kingdom, for example – while elsewhere less draconian non-pharmaceutical interventions (NPIs) have been tightened. The intention is to reduce the number of new cases below the point where the healthcare systems will be overwhelmed. However, side by side there is an urgent need to tailor interventions and prevent economic devastation due to the failure of more businesses, with general slowing down of the economy.
The current wave goes back to the summer, when NPIs were relaxed all over Europe. Many small outbreaks followed this as the virus began to show community spreads.
Uniform pattern among European populations
A variant of SARS-CoV-2 has been reported to be isolated from Spanish samples at the beginning of summer, spreading throughout Europe subsequently. Beginning with farm workers in northeastern Spain, this moved to the local community and then throughout Spain.
Reports show that while the disease first appeared to spread within the age groups 15-24 and 25-34 years, it spread mostly in the former group as summer progressed. This pattern seems to be common throughout Europe in the second wave. In almost every country, those most affected were between 18-29 years of age.
There was no marked rise of incidence among the elderly, as happened in the first wave, and children formed a very small proportion of the infected population. And finally, the involvement of this group, in a uniform pattern throughout Europe, contrasts strongly with the different peaks and periods observed with the first wave.
The researchers suggest that this regularity in the pattern of age-specific case rises – due to the common causes and similar routes of viral spread – is being seen not only in most European countries but also in the USA.
What caused uniformly higher incidence in young adults?
One reason could be that universities and schools reopened at this time.
Another could be that this age group has its own behavioral features, in which case the national culture, NPIs and demographic characteristics would be less relevant.
Young people in this group feel invulnerable, in general, and are less compliant with social isolation measures. They are, perhaps, the group with the highest mobility and the most diverse contacts, and so their lifestyle predisposes them to viral transmission. This could be why, as the researchers point out, “the high incidence in younger people does not propagate to other age groups.”
What are the implications?
Understanding such features could be key to teasing out the most important factors driving the second wave. This will determine what areas need to be targeted in controlling the epidemic.
The researchers suggest several implications of their findings. First, it is essential to achieve lower transmission in young adults. One way to do this is by better communication with this group. The aim should be to show them the scientific underpinnings of NPIs, their relevance, and their importance. Such education should help them to change their behavior to reduce the transmission and number of new cases among them.
Secondly, the study seems to confirm that viral transmission is uneven across age groups, since children are less commonly infected. This point is important in deciding whether schools should be reopened or not.
It is quite possible that, as the authors suggest, the low rate in children could be due to their protection by the policies currently being followed. Another hypothesis is that children are either less susceptible or are tested far less frequently, due to a higher proportion of asymptomatic infection.
If the second was the case, these asymptomatically infected children would transmit the disease to their parents, which means a high incidence among the age groups to which their parents belong. Since this belies the commonly observed trend, the first reason (lower susceptibility in children) seems to be more probable.
Moreover, this would suggest that schools could remain open, since being able to attend schools is ostensibly among the most significant social benefits a society can offer its children.
The researchers sum up, “These results could help understand what are the main drivers of the second wave and to better design and adapt public health interventions during this stage of the pandemic.” On the other hand, these findings also emphasize the need to study the chain of transmission so as to understand how the infection spreads in different age groups. This will necessitate the generous and unrestricted sharing of data on the population affected by the virus to refine and extend such studies.
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.